Synthesis gas is produced from hydrocarbons by steam reforming by the reactions (1)-(3): EQU C.sub.n H.sub.m +n H.sub.2 O.fwdarw.n CO+(n+m/2) H.sub.2).DELTA.H.degree./298&lt;0) (1) EQU CO+H.sub.2 O.revreaction.CO.sub.2 +H.sub.2 (--A.DELTA.H.degree./298=41 kJ/mol) (2) EQU CH.sub.4 +H.sub.2 O.revreaction.CO+3 H.sub.2 (--.DELTA.H.degree./298=0.206 kJ/mol) (3)
State of the art steam reforming technology makes use of reforming catalyst in the form of pellets of various sizes and shapes. The catalyst pellets are placed in fixed bed reactors (reformer tubes). The reforming reaction is endothermic. The necessary heat for the reaction is supplied from the environment outside of the tubes usually by a combination of radiation and convection to the outer side of the reformer tube. The heat is transferred to the inner side of the tube by heat conduction through the tube wall, and is transferred from the gas phase to the catalyst pellet by convection. The catalyst temperature can be more than 100.degree. C. lower than the inner tube wall temperature at the same axial position of the reformer tube. Below this is called conventional reforming.